1. Field of the Invention
The present invention relates generally to an apparatus for receiving broadcasting signals, and more particularly, to a broadcasting signal receiving apparatus which is operative to receive a digital audio broadcasting signal and to carry out a digital transmission of a digital audio signal and service data which are obtained based on the digital audio broadcasting signal received thereby.
2. Description of the Prior Art
Although an analog audio broadcasting system which includes an amplitude-modulated (AM) audio broadcasting system in which audio information signals are transmitted in the form of an AM audio information signal and a frequency-modulated (FM) audio broadcasting system in which audio information signals are transmitted in the form of a FM audio information signal, has been put to practical use for a long time in the field of audio broadcasting, there has been recently proposed the introduction of a digital audio broadcasting system in which audio information signals are transmitted in the form of a digital audio information signal for the purpose of improving quality of audio information transmitted or received in the system. In particular, in the European Continent, the digital audio broadcasting system called "DAB" has been already put to practical use in some countries.
It is expected that the digital audio broadcasting system would have great development henceforth so as to be in the mainstream in the field of audio broadcasting, in place of the analog audio broadcasting system, some time in the not so far future. However, at present, in a region wherein the digital audio broadcasting system has been already put to practical use or has been concretely planed to be materialized, a service area in which the digital audio information signal transmitted from a broadcasting station can be properly received is restricted to be relatively small. Therefore, in the case where the digital audio broadcasting is actually carried out, the analog audio broadcasting is also carried out, in addition to the digital audio broadcasting, so that the same program is transmitted through each of the digital audio broadcasting and the analog audio broadcasting at the same time.
The digital audio broadcasting signal carries not only audio information data forming a digital audio signal but also service information data representing, for example, weather forecast, traffic information and so on, and further carries control information which are necessitated for reproducing the digital audio signal from the audio information data and the service information from the service information data on the receiving side. Such digital audio broadcasting signals are received by use of a digital audio broadcasting signal receiver.
In the digital audio broadcasting signal receiver, each of digital audio broadcasting signals transmitted respectively from a plurality of broadcasting stations is received selectively through a tuning operation by a tuner, the received digital audio broadcasting signal is subjected to a demodulation processing in a channel decoder and subjected also to a data selection processing in a program selector so as to produce the control information, service information data and audio information data, and the audio information data obtained from the program selector is subjected to a decoding in a source decoder so that the digital audio signal is reproduced. Then, digital transmissions of the digital audio signal reproduced in the source decoder, the control information obtained from the program selector and the service information data obtained from the program selector are carried out to some other device or apparatus connected to the digital audio broadcasting signal receiver.
FIG. 1 shows an example of the digital audio broadcasting signal receiver proposed previously and generally. In the digital audio broadcasting signal receiver shown in FIG. 1, a digital audio broadcasting signal transmitted from a broadcasting station and having reached a receiving antenna 11 is received through a tuning operation by a tuner 12. In the tuner 12, the received digital audio broadcasting signal is subjected to an amplifying processing and a frequency-converting processing to produce an intermediate frequency (IF) signal Sid. The IF signal Sid is supplied to an analog to digital (A/D) convertor 13. A digital IF signal Did corresponding to the IF signal Sid is obtained from the A/D convertor 13 to be supplied to a channel decoder 14.
In the channel decoder 14, the digital IF signal Did is subjected to a demodulation processing to produce control information data representing the control information, audio information data and service information data. Further, in the channel decoder 14, the audio information data and service information data are subjected respectively to time de-interleaving arrangements, and the control information data and the time de-interleaved audio information data and service information data are subjected respectively to error correction processings. Then, the control information data Dcd subjected to the error correction processing are supplied from the channel decoder 14 to a control unit 15 and a service data producing portion 16, and composite data Dmd containing the audio information data and service information data each subjected to the error correction processing is supplied from the channel decoder 14 to a program selector 17.
In the program selector 17, the audio information data and service information data are separately derived from the composite data Dmd. Then, audio information data Dad are supplied from the program selector 17 to a source decoder 18 and service information data Dsd are supplied from the program selector 17 to the service data producing portion 16.
In the source decoder 18, the audio information data Dad subjected to the error correction processing are subjected to a decoding to produce a digital audio signal Da. The digital audio signal Da thus obtained from the source decoder 18 is supplied to both a digital/analog (D/A) convertor 19 and a digital audio signal transmission processor 20.
The D/A convertor 19 is operative to cause the digital audio signal Da obtained from the source decoder 18 to be subjected to a D/A conversion to produce an analog audio signal Sa and to derive the analog audio signal Sa to an audio signal output terminal 21.
The digital audio signal transmission processor 20 is operative to produce a digital transmission signal Dat for digital transmission of the digital audio signal Da obtained from the source decoder 18. The digital transmission signal Dat produced in the digital audio signal transmission processor 20 is supplied through a driving portion 22 to a digital output transmitter 23.
The digital output transmitter 23 is operative to obtain, based on the digital transmission signal Dat from the driving portion 22, a digital transmission light output Pat for carrying out the digital transmission of the digital audio signal Da obtained from the source decoder 18 and to forward the digital transmission light output Pat to a digital transmission path 24, such as a digital optical transmission path.
In the service data producing portion 16 to which the control information data Dcd obtained from the channel decoder 14 and the service information data Dsd obtained from the program selector 17 are supplied, service data Ds are produced based on the control information data Dcd and service information data Dsd to be supplied to a service data transmission processor 25.
The service data transmission processor 25 is operative to produce a digital transmission signal Dst for digital transmission of the service data Ds obtained from the service data producing portion 16. The digital transmission signal Dst produced in the service data transmission processor 25 is supplied through a driving portion 26 to a digital output transmitter 27.
The digital output transmitter 27 is operative to obtain, based on the digital transmission signal Dst from the driving portion 26, a digital transmission light output Pst for carrying out the digital transmission of the service data Ds obtained from the service data producing portion 16 and to forward the digital transmission light output Pst to a digital transmission path 28, such as a digital optical transmission path.
The control unit 15 produces control signals Cc and Cp in response to the control information data Dcd obtained from the channel decoder 14 and supplies the channel decoder 14 with the control signal Cc for controlling thereby the operation of the channel decoder 14 and the program selector 17 with the control signal Cp for controlling thereby the operation of the program selector 17.
In general, the digital transmission light output Pat transmitted through the digital transmission path 24 in the form of, for example, the digital optical transmission path and the digital transmission light output Pst transmitted through the digital transmission path 28 in the form of, for example, the digital optical transmission path are supplied to some other device or apparatus which is connected to the digital audio broadcasting signal receiver shown in FIG. 1 and used selectively in accordance with the other device or apparatus. For example, when the other device or apparatus is an audio signal amplifier connected to the digital audio broadcasting signal receiver shown in FIG. 1, the digital transmission light output Pat transmitted through the digital transmission path 24 is amplified by the audio signal amplifier to be used for reproducing an analog audio signal, and when the other device or apparatus is a navigating apparatus for vehicles connected to the digital audio broadcasting signal receiver shown in FIG. 1, the digital transmission light output Pst transmitted through the digital transmission path 28 is received by the navigating apparatus for providing it with information for navigation.
In the digital audio broadcasting signal receiver shown in FIG. 1, a series connection of the driving portion 22 and the digital output transmitter 23 coupled to the output end of the digital audio signal transmission processor 20 are necessary for forwarding the digital transmission light output Pat to the digital transmission path 24 in response to the digital transmission signal Dat from the digital audio signal transmission processor 20, and further a series connection of the driving portion 26 and the digital output transmitter 27 coupled to the output end of the service data transmission processor 25 are also necessary for forwarding the digital transmission light output Pst to the digital transmission path 28 in response to the digital transmission signal Dst from the service data transmission processor 25.
The series connection of the driving portion 22 and the digital output transmitter 23 and the series connection of the driving portion 26 and the digital output transmitter 27 can be formed to have the same structure as each other. This means apparently that a couple of circuit portions capable of having the same structure are provided for forwarding the digital transmission light outputs Pat and Pst to the digital transmission paths 24 and 28, respectively.
Besides, the digital transmission light outputs Pat and Pst transmitted respectively through the digital transmission paths 24 and 28 are usually used selectively in accordance with an electronic apparatus connected to the digital audio broadcasting signal receiver shown in FIG. 1. That is, usually the digital transmission light outputs Pat and Pst transmitted respectively through the digital transmission paths 24 and 28 are not used at the same time but used with seperately.
Since a couple of circuit portions capable of having the same structure are provided for forwarding the digital transmission light outputs Pat and Pst to the digital transmission paths 24 and 28, respectively, as aforementioned, there is room for improvement to simplify the circuit portions so as to have an improved coefficient of utilization and to reduce the cost thereof in the digital audio broadcasting signal receiver shown in FIG. 1.